The present invention concerns the processing of colour reversal photographic film with a low water consumption. More particularly, the invention concerns a method which enables the water consumption of washing baths to be limited, the water supply of the washing baths being maintained by a counter-current coming from the bath placed downstream, the excess volume of water being discharged through an overflow. The wash waters are recovered and purified by a single nanofiltration device capable of giving a permeate which can be recycled to the washing baths of the treatment. The method of the invention also makes it possible to overcome the problems of the discharge of chemical substances to the drains while maintaining good sensitometry of the developed films.
The invention also concerns a device for implementing the process.
A conventional method for processing an exposed reversal colour film comprises successively a black and white development step, a chemical reversal step (or fogging exposure) and a color development step. The chemical reversal step or the fogging step makes it possible to develop the silver halides which had not been initially exposed. Such a processing for colour reversal films is well known and is described in detail in xe2x80x9cChimie et Physique Photographiquesxe2x80x9d volume 2, P. Glafkidxc3xa8s, 5th edition, Chapter XL, pages 947-967.
An example of such a processing method for a colour reversal film is the Ektachrome E-6(copyright) processing described in detail on page 954 of Glafkidxc3xa8s aforementioned book.
In the Ektachrome E-6(copyright) processing, the exposed photographic material passes successively through each of the following baths:
a) a black and white development bath,
b) a first washing bath,
c) a chemical reversal bath,
d) a color development bath,
e) a conditioning bath,
e) a bleaching bath,
f) a fixing bath,
g) one or more washing baths, and
h) a rinsing bath.
These are followed by a drying step.
When the photographic material passes from tank to tank, considerable quantities of chemicals are entrained from one tank to another either by the photographic material, or by conveyor belts which are used for moving the photographic material. These chemicals accumulate in the baths, reducing the efficiency thereof. Entrainment of these chemicals increases as the processing of photographic materials becomes more rapid.
The chemical contamination of the first washing bath comes from:
the 1st developer by entrainment of chemical substances, and
the reversal bath, due to the maintenance of the water level of the first washing bath by a counter-current coming from the reversal bath.
The chemicals can be organic contaminants, such as the conventional constituents of black and white developers, for example metol, hydroquinone, phenidone, potassium hydroquinone monosulfate, 4-(hydroxymethyl)-4-methyl-1-phenyl-3-pyrazolidone (HMMP), or propionic acid. The chemicals can be inorganic contaminants, such as tin (II), coming from the reversal bath, as well as iron and halides.
In order to minimize the contamination of baths by these chemicals, it is known to use a regenerating solution. In practice, the regenerating solution is introduced into the contaminated bath to be regenerated and an equivalent volume of the exhausted bath is discharged through an overflow. This method generates a considerable volume of exhausted baths which can no longer be used photographically.
Another known method for minimizing the entrainment of chemicals consists of renewing the washing baths by adding thereto clean water continuously so as to maintain a very low concentration in chemicals in these washing baths. For example, it is known to place a first washing bath between the first black and white development bath and the chemical reversal bath. The purpose of this first washing bath is to interrupt the chemical reactions due to the first development bath and to prevent the migration by entrainment of the first developer to the reversal bath, preventing in this way a deterioration of the quality of the image of the developed film. Thus for a standard Ektachrome E-6(copyright) washing baths, a continuous supply of water which up to a flow rate of 7.5 liters per minute is currently used. This method therefore involves a large consumption of water, increasing in this way the cost of the processing. Moreover, development laboratories must now comply more and more with increasingly strict regulations which very closely limit the consumption of water per square meter of the developed films.
Similarly, in order to limit the consumption of water of mini-laboratories for the treatment of colour reversal photographic films, it is known to maintain the level of water in each washing bath by a counter-current coming from a bath downstream, and to discharge an equivalent volume of water into a reservoir by means of an overflow, while maintaining a supply of water for the final rinsing bath. This processing of exposed reversal colour films is used in mini-development laboratories (more commonly called a minilab) and comprises baths in the following order:
a) a black and white development bath,
b) a first washing bath, initially filled with clean water, of which the water level is maintained by a counter-current coming from the reversal bath and an equivalent volume of water is discharged by means of an overflow,
c) a chemical reversal bath,
d) a color development bath,
e) a conditioning bath,
f) a bleaching bath,
g) a fixing bath,
h) at least two final washing baths, the water level of which is maintained by a counter-current coming from a rinsing bath placed downstream, and
i) a final rinsing bath supplied with water from an auxiliary source. The drying step is then carried out.
However, one of the problems encountered by this type of installation is the accumulation with time of organic and inorganic contaminants in the baths, in particular in the washing baths. The washing baths cannot then be discharged to the drains and must be decontaminated first. Moreover, the accumulation of certain contaminants brings about harmful effects on the sensitometric quality of the development of the films. For example, when the tin (II) concentration is too high in the first washing bath, a very harmful effect is observed on the sensitometry of the developed films. In general, for this type of minilab, when a concentration of tin (II) is in excess of 400 ppm in the first washing bath, the sensitometry of the developed films is degraded. In order to overcome this problem, it has been proposed to use a flow of air bubbles so as to oxidize the tin (II) to tin (IV) which is less harmful for the sensitometry of the films to be developed. However, this type of technique brings about the formation of foam on the surface of the baths even when anti-foam agents are used. The formation of foam in processing baths should be avoided because it adds a source of contamination of the adjacent baths by overflow. Moreover, the accumulation of organic substances (black and white developers, co-developers etc) as well as the stream of air bubbles, favors the formation of biofilms in the first washing bath which can then contaminate the other baths of the processing by entrainment, either by the photographic material or by the belts conveying the photographic material. The formation of biofilms also causes a clogging of the cleaning filters of the tanks as well as the emission of nauseating odours. It is therefore necessary to perform frequent maintenance and cleaning operations involving numerous stoppages of the minilab.
Taking into account the above-mentioned problems, there is a need of systems for treating and recycling waters coming from the washing baths, as completely as possible, while keeping the level of chemical contaminants as low as possible in the washing baths and in particular in the first washing bath. It is particularly desirable for the tin (II) level to remain below 400 ppm in the first washing bath so as to maintain an acceptable quality of the sensitometry of the developed films.
One object of the present invention is to do away with the air bubbled through the first washing bath, and the formation of biofilms and foam.
Another object of the invention is to provide a method and a device for treating a colour reversal photographic film enabling a significant reduction to be made in the consumption of treatment water, as well as the volume of photographic effluents, and this without degrading the sensitometry of the developed films.
Another object of the invention is a photographic processing method which enables discharges of chemical substances to the drains to be reduced.
Still further objects will be apparent in a detailed manner in the following description.